The present invention relates to a process of producing a gold decorative item and a gold decorative item so produced.
According to the invention, there is provided a process of producing a gold decorative item, comprising the steps in sequence of producing an alloy of gold, silver, copper and zinc, forming the gold alloy into a specific shape according to the design of the decorative item and polishing the surface of the decorative item so formed, submerging the decorative item in an acid solution for etching its surface to form a scale pattern, and submerging the decorative item in an alkaline solution for removing unwanted substances formed on the surface during etching.
Preferably, the acid solution is a solution comprising hydrochloric acid and nitric acid.
More preferably, the ratio by part of the hydrochloric acid to the nitric acid falls within the range from 3:1 to 5:1, with their concentrations being in the ranges of 30% to 50% and 55% to 75%, respectively.
It is preferred that the alkaline solution is a solution of sodium cyanide.
It is further preferred that the sodium cyanide solution has a concentration over 90%.
Advantageously, the process includes an additional step of applying ultrasonic irradiation to the decorative item when the item is submerged in the alkaline solution.
Preferably, the process includes a subsequent step of submerging the decorative item in second acid solution at an elevated temperature for removing low-value metals.
More preferably, the second acid solution comprises hydrosulphuric acid.
It is preferred that the alloy includes palladium.
In a preferred embodiment, the percentages by weight of the components of the alloy are in the ranges of 75% to 78% for gold, 13% to 18% for silver, 3% to 5% for copper, and 2% to 4% for zinc.
In another preferred embodiment, the percentages by weight of the components of the alloy are in the ranges of 75% to 78% for gold, 11% to 16% for silver, 4% to 6% for copper, and 2% to 3% for zinc.
More preferably, the alloy includes palladium at a percentage by weight in the range of 5% to 10%.
The invention also provides a gold decorative item produced by the aforesaid process, wherein the alloy includes palladium.
As an example, the percentages by weight of the components of the alloy are in the ranges of 75% to 78% for gold, 13% to 18% for silver, 3% to 5% for copper, and 2% to 4% for zinc.
As another example, the percentages by weight of the components of the alloy are in the ranges of 75% to 78% for gold, 11% to 16% for silver, 4% to 6% for copper, and 2% to 3% for zinc.